A teenager convicted of fatally shooting a baby in a stroller has been sentenced to spend the rest of his life in prison with no chance of parole after the grieving mother asked a judge to punish the gunman for taking "the love of my life".

De'Marquise Elkins, 18, stood silent and showed no emotion as he was sentenced in a courtroom less than two weeks after a jury found him guilty of murder in the slaying of 13-month-old Antonio Santiago during a robbery attempt.

"His first word was never heard. His first sentence was never said," Sherry West, the baby's mother, said through tears on the witness stand as she read a statement made to rhyme like a poem or a nursery rhyme. "He never got to sleep in a toddler bed."

The baby was in his stroller and out for a walk with his mother when he was shot between the eyes March 21 in the Georgia coastal city of Brunswick.

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West and a younger teenager charged as an accomplice testified at trial that Elkins killed the baby after his mother refused to give up her purse.

Elkins was spared the death penalty because the killing occurred when he was 17, which the US Supreme Court has ruled is too young to face capital punishment. Under Georgia law, the only possible punishments for Elkins were life with or without a chance of parole.

But Elkins' defence attorneys told Judge Stephen Kelley that life without parole was too harsh for such a young defendant. They introduced court documents from the past seven years showing Elkins had been neglected by a mother who struggled with drug abuse and sometimes left him home alone without food.

The judge not only gave Elkins the maximum possible punishment for his murder conviction, but also sentenced him to 105 additional years in prison for other counts including aggravated assault and attempted armed robbery.

That included 30 years for shooting and wounding a pastor outside his church 10 days before the baby was killed.

"We're definitely disappointed with the ruling," defence attorney Kevin Gough said as he left Glynn County Superior Court. "Life without parole for a juvenile, our position remains, is cruel and unusual punishment."

Gough said he plans to appeal both the verdict and the sentence. Elkins would have been eligible for parole in 30 years had that been allowed as part of his sentence.

Ultimately the judge sided with prosecutors who urged him to consider the brutal circumstances of the crime and that Elkins escaped facing the death penalty only because he shot the baby a few months shy of his 18th birthday.

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"He aimed that gun right between that baby's eyes and shot that baby," District Attorney Jackie Johnson said. "I don't know of a more inhumane act or wantonly vile act ... than to aim a gun at a sleeping baby in a stroller and take that baby's life."

At trial, prosecutors had said West was pushing her son in his stroller home that March day from a post office when two teenagers approached her, blocks from her apartment.

Dominique Lang, 15, testified at trial he was with Elkins when the older teen pulled a gun and demanded West's purse. When she refused, Lang said, Elkins twice threatened her baby and counted down from five.

West testified she pleaded with Elkins that she had no money and tried to cover her child with her arms as the gunman fired a warning shot, fired a bullet into her leg and then shot the baby.

Police recovered a .22-caliber revolver from a pond, and prosecutors said it matched the gun used in the killing.

Lang also faces murder charges. No trial date has been set and it's unknown how his cooperation in the Elkins prosecution might affect his case.

- AP